1. Field of the Invention
This invention relates to a stem for semiconductor laser devices.
2. Description of the Prior Art
Semiconductor laser devices have such advantages that they are compact and highly efficient in energy conversion in comparison with other laser apparatus, and that the lased light from the laser devices can be directly modulated by the driving current. Therefore, they are promising in the use of light sources for optical information data processing. It is required for such application purposes that the semiconductor laser device stably issues lased output of the fundamental transverse mode. Most semiconductor laser devices generally generate substantially linearly polarized light as lased light. And in the cases that they are used as light sources in the application fields related with optical information data processing, it is necessary that the polarization direction is known to the users when mounting in optical apparatus.
In addition, when stems for the semiconductor laser devices are mounted in various optical apparatus, it is necessary to adjust the polarization direction of the linearly polarized light so that the lased light propagates at a specified direction. In this case, it is preferable to employ a stem configuration where the polarization direction of the lased light is set to be parallel to (or perpendicular to) a certain reference face of the stem of the semiconductor laser device. By employing such a configuration it becomes much easier to adjust the polarization direction of the lased light in the optical device.
Recently, various semiconductor laser devices formed on substrates having a novel terraced structure have been proposed in several U.S. patent applications by the same assignee as that of the present invention (e.g. T. SUGINO et al., Ser. No. 40,182 filed on May 18, 1979, now U.S. Pat. No. 4,296,387). It is possible to obtain stable fundamental transverse mode oscillation by such semiconductor laser device where the active layer lies on a plane making a specified angle against the horizontal face of the semiconductor substrate.
FIG. 1 is a cross-sectional view of a semiconductor laser device formed on a substrate 1 having a terraced structure. The semiconductor laser device comprises a substrate 1 of the terraced structure, which has a step 101, clad layers 2 and 4, an active layer 3, a cap layer 5, and electrodes 6 and 7. In general, a polarization direction of the lased light from semiconductor laser devices is parallel to the active layer. This means that the polarization direction (indicated by an arrow ".gamma.") of the semiconductor laser device shown in FIG. 1 makes a specified angle against the horizontal face of the substrate 1. The semiconductor laser device of FIG. 1 has been mounted on a stem shown in FIG. 2.
The stem shown in FIGS. 2(a) and 2(b) is made up of a base plate 8 and a heat sink block 9 on which a semiconductor laser device 10 with a terraced structure is bonded. The heat sink block 9 is soldered to the base plate 8 which is provided with holes 11 for fixing the base plate 8 at an external heat sink.
When the semiconductor laser device 10 of FIG. 1 is mounted on the stem having a bonding face parallel to a stem base line A--A' shown in FIG. 2 (where FIGS. 2(a) and 2(b) are a front view and a side view of a conventional stem for a semiconductor laser device, respectively), the polarization direction indicated by an arrow ".gamma." becomes tilted against the stem base line A--A'. Accordingly, in case the stem shown in FIGS. 2(a) and 2(b) is mounted in optical apparatus in such a manner that the stem base line A--A' lies parallel to a base face of the optical apparatuses, for example parallel to the horizontal face, then a polarization direction of the lased light becomes tilted from the horizontal face. But, this situation is not appropriate, since it is not easy to adjust mounting positions of optical devices employed in the optical apparatuses by use of a tilted reference line. For example, it is not easy to adjust the optic axes of polarization prisms and wave plates with respect to the polarization direction of the based light.